Magnetic clamping appliance



July 30, 1940. J. BING ET A1. 2.209,558

MAGNETIC CLAMPING APPLIANGE Filed May 19, 1938 1b 1 4 N |A N |-15a- Patented July 30, 1940 PATENT cerise;

MAGNETIC CLAMPlN G CE Julius Bing and Otto Block, Berlin, Germany, as= signora to Karl Otto Goettsch, Siivahoi, Bern,

Switzerland Application May 19, 1938, Serial No. 208,947 In `Germany April 22, 1937 9 Claims.

Our invention relates to magnetic clamping appliances, such as are mainly used in connection with machine tools, particularly grinding machines, for nxing the work.

5 In general in such appliances the magnet is excited by continuous current, that is, by electromagnetic means. It has however also already been proposed to provide for this purpose permanent magnets of very great coercive force,

lo which usually consist oi' an alloy of aluminium, nickel and iron, with certain other additions. Now in such holding devices the removal of the work gives rise to difficulties on account of the g so-called residual magnetism remaining in them 1I and also in the soft iron parts oi the apparatus even after the cessation of the magnetic excitation, owing to the permanent magnet. Furthermore the known clamping devices of this nature require the exertion of comparatively large m forces in the relative displacement between the permanent magnets and the associated soft iron parts of the magnetic circuit, this displacement bringing about the excitation and cle-excitation.

The principal object of our invention is to g5 provide a magnetic clamping appliance of the permanent magnet type in which the said disadvantages are obviated. A further object is to provide a clamping appliance of the class referred to in which a better utilisation of the space availn able is obtained. Still a further object is to provide a clamping appliance of the permanent magnet type which easily may be manufactured on mass production lines.

With these and other objects in view, which u will appear from the following description taken in connection with the drawing, our invention is essentially characterised by the feature that in a magnetic clamping device of the perma-V nent magnet type the parts that are displacen able relatively to one another for the excitation and deexcitation of the magnetic system or systems can be rotated so far beyond the relative positions corresponding to the short-circuiting of the permanent magnet or magnets that not only does the magnetic inuence of the perma` nent magnet or magnets upon the other members of the magnetic circuit or circuits become a minimum, but a reversal of polarity is also eilected, whereby the result is reliably obtained that the attraction exerted upon the work assumes a zero value.

A further feature ot our invention resides in the fact that the permanent magnet or magnets are constructed as revolving bodies, the axes of u which are transverse to the lines of force passing spending bores in cover plates il and i2:

(Cl. 17E-367) through the revolving bodies in a substantially unaltered directionI and that the supporting the revolving bodies in relation to the associated parts of the magnetic circuit in question effected in such a way that the magnetic forces exerted upon them substantially ccunterbelanc one another, so that for the shifting of the rotar bodies only very small forces are required.

Further features and advantages ci our innenu tion will be gathered from the ensuing description and the claims attached thereto.

In the accompanying drawing, in which so preferred forms oi.' construction of the i clamping appliance are illustrated by way e example, 11n

Figure 1 shows a sectional elevation transverse to the axes of rotation ci the magnet had through a portion of the clamping appliance' Figure 2 is a similar view showing a met form of construction;

Figure 3 is a view from l new clamping appliance;

Figure -i is a vertical section thrcug" axes of rotation of the permanent i showing the end parts of an applies a clamping plate according to Figure mounted, and

Figure 5 is an end view ci an embodiment a clamping appliance consisting or" e. single net unit.

In the embodiment illustrated in 'figur upon a base plate I of non-magnetic mais is mounted a number of magnet unite conesponding to the length of the clamping ance, these units being denoted by the nur 2, 3, 4 and so forth. The individuai mainly consist in each instance of telo limo 2b 3a, 3b and so forth of soft iron, and oi manent magnets 5, 5a, 5b and so orth mounted between the said pairs el limbs. spaces between the upper ends of the lim filled up, in a manner known in connection magnetic clamping plates, by bars ile, so forth of non-magnetic material.

'I'he permanent magnet bodies in 'ia-he bodiments` illustrated. form circuler with diametrically opposite dats, which however alternatively be omitted. They ported with minimum clearance between the indrically hollowed limbs, this being chi either in the manner indicated in 'ideare l the aid of special pivots passing through cc ends of the magnet units, or else by the magnet bodies themselves being supported by their peripheries in the cylindrical cavities (pole arcs) Yof the magnet limbs pertaining to them. They then form as it were their own bearing journals, while the pole arcs constitute the bearing bushings. The cavities formed on the one hand by the magnet limbs 2a, 2b, 3a, and 3b and so forth, their connecting bars 8, 8a, 8b and so forth, and the base plate I, and on the other hand by the end cover plates II, I2 are preferably filled with oil or solid grease, as a result of which inthe first place the rotary bodies are lubricated in their bearings formed by the pole arcs, and on the other hand the penetration of dust from grinding, moisture or the like into the interior of the units is prevented. Lubricating nipples l, l, shown in Figure 4, may be provided for the purpose of moving the oil or grease to and fro.

As indicated in Figures 1 and 2 by incomplete dotted circles, and as shown clearly in Figure 4, toothed wheels I3 are rigidly connected with the permanent magnet bodies 5, 5a, 5b and so ripheral arcs facing one another are marked N and S.' In the position of the magnet cores illustrated in Figure 1 the lines of force meet with comparatively little reluctance at the air gaps between the cylindrical portions of the magnet coresand the pole arcs facing them of the limbs 2a, 2b and so forth, so that if there is a workpiece W of magnetic material upon the top of the magnet iimbs, which is ground smooth in the usual way, strong systems of lines of force` are produced, whichtake the course indicated by dotted lines, so that the work W is powerfully attracted.

If the work is to be removed after termination of the grinding or the like, all the magnet cores 5, 5a, 5b and so forth are rotated through an angle 'of about 90 in the direction of the arrows in Figure 1 in the manner described above by means of a crank to be mounted upon theV square stud ifi. The magnetic flux then becomes gradually weaker, since the reluctances between the overlapping parts of the poles of the magnet cores on the Aonehand, and of the pole arcs of the magnet limbs on. the other hand a. 'are continually becoming greater. After a rotation of 90 the magnet cores are magnetically short-circuited by the associated magnet limbs and the actions of the pairs of flux systems then arising counteract one another. In consequence ofthe residualmagnetism both of the limbs of the magnets and of the workpiece, however, the latter still adheres, so that the removal causes difficulties in some circumstances. In order to eliminate even the last traces of magnetism all that is necessary is to rotate the magnet cores 5, 5a, 5b and so forth through a small angle further. VThe leakage flux passing through the limbs of the magnets and through the work then increases again. Now however the lines of force are in the reverse direction, so that the residual have more poles.

`magnetism can be caused to disappear completely. After putting on fresh workpieces the magnet cores 5, 5a, 5b and so forth are brought back by suitable rearward rocking into the original position (Fig. l), in which the iiux systems are completely restored, so that the workpieces are securely xed again.

In the form of construction illustrated in Figure 2 the foot plate consists of magnetic material, for instance iron. Here the magnet cores 5, 5a, 5b, 5c and so forth, likewise constructed as cylinders, are supported between the pole arcs, located perpendicularly one above another, of the magnet limbs 2a, 2b and so forth, the latter of which are mounted directly upon the base plate I. In this manner the iiux systems are formed in the paths indicated by dotted lines. For the rest the manipulation and action are the same as in the case of the construction illustrated in Figure 1.

Our invention is not restricted tothe bi-polar magnet systems illustrated, but the permanent magnets may instead be so magnetised as to In a four-pole system oi' magnets the rotation of the permanent magnet bodies through an angle of 90 at most would be suiiicient to attain with certainty, after the short-circuiting, also the reversal of polarity faf cilitating the removal of the workpieces.

The alloys used as material for the permanent magnets are very dimcult to work. For this reason it may be advisable, at least when the shape of the magnet bodies is not very simple, to lodge the alloys in a granulated condition in thinwalled sheaths which are shaped to correspond to the desired form of the magnet bodies. For example instead of the solid cylinders described. consisting of the alloy material, thin-walled hollow cylinders of iron might be employed, which are lled with granulated alloy material, with the addition, it may be, of binding agents. The positive mutual connection of the permanent magnet bodies, which ensures the identity of their displacement movements, may of course be obtained otherwise than by means of interengaging toothed wheels, for instance by means of levers, toothed racks and the like.

Magnetic clamping appliances of the kind described, as contrasted with those hitherto usual, admit of being very easily manufactured on mass production lines. ,For this purpose a start is made from the individual units, which form as it were the foundation-elements of a clamping Y posite open ends are then covered by cover plates of non-magnetic material of the nature of the plates II and i2 represented in Figure V4, which may serve at the same time for supporting the permanent magnets 5. The magnet limbsZa, 2b, 3a, 3b and so forth, may be formed in the simplest manner from sections of suitable drawn prole material. To the units there may also pertain the foot plates, which mechanically connect the lower ends of the limbs of the magnets with one another but insulate them magnetically, as indicated in Figure 1V by the dotted lines passing through the plate I and forming a continuation of the joints between the individual devices. 'I'he units would then have to be mounted also upon a separate bottom plate extending throughout the entire length of the apparatus.

In order to have available for the machining of relatively small workpieces as fine a subdivision of poles of the actual clamping surface as possible, it is advisable to equip the clamping appliance with one or more separate clamping plates, which are mounted as required upon the surface of the magnet limbs, which ordinarily themselves serve "as a clamping plate, and which are connected with one another by the magnetically insulating intermediate bars I.

These special clamping plates are composed, as illustrated more particularly by Figures 3 and 4, of numerous comparatively narrow strips or square rods I5, IB of alternately magnetic and non-magnetic material, for instance iron and' brass. The iron rods I5 are provided at distances from one another corresponding to the subdivision of the top of the clamping appliance. with downwardly directed projections IIb, which are separated from one another by shallow recesses lia. 'I'he length of the projecting portions Ib corresponds to the breadth of the portions of the magnet limbs 2a, 2b located in the surface of theclamping appliance. 'I'he clamping plate composed of the rods I5 and Il and denoted as a whole by I1 is so placed upon the surface of the clampingI appliance that the said rods extend at right angles to the axes of rotation of the magnet cores 5, and therefore also to the joints parallel thereto in the top of the appliance. By varying the breadth on the one -hand of the iron rods and on the other hand of the brass rods, the clamping plate can be adapted to the most varied requirements, particularly as regards the size of the workpieces.

In Figure 5 is represented a particular embodiment of the clamping appliance, which consists of one unit only, this unit being oi' comparatively small length, so as to yield a magnetic system of substantially cubic shape. The construction of the magneticsystem is the same as has been described above. I'he unit rests by its base plate I upon the flange Il oi a holder Il, which may conveniently form a square stud, and which serves for clamping between the jaws of a vice or the like. The base plate I is connected with the holder I! by means of a screw 20, which is accessible through a bore in the holder X pin I9, and which permits rotation of the clamping appliance 2 itself, in relation to the 'holder I8, Il. A device is preferably also provided which enables the clamping appliance 2 to be secured in various angular positions. Such a device may consist for example of a drag spring, lodged in the flange I9, and acting upon the base plate I. In Figure 5 merely a set screw 2l is provided for this purpose.

It may be observed that the construction of the permanent magnet as a simple solid of revolution, particularly in the form of a cylinder, yields remarkably short paths for the lines of force, which is of great importance on account of the small magnetic permeability of the highly coercive material used for the permanent magnets.

We claim:

1. In a magnetic clamping appliance; a magnetic circuit comprising a rotatable substantially cylindrical permanent magnet, two soft iron bodies having cylindrical pole-arcs disposed 0pposite each other and snugly fitting with the tances between the limbs being dimensione cylindrical surface of said permanent i so as to form a Journal-bearing for tl: and means to rotate said permanent mag@ 2 .A clamping appliance as claimed in c characterised by the feature that the sci bodies are connected one to the other net. and being adapted to be filled, with la 3. In a magnetic clamping appliance, s.. netic circuit comprising a substantiail such a way that the lines of force it substantially diametrically and at right to its axis of rotation, and two soit each having a cylindrical hollow pola-arc ing with the permanent magnet a cyiinai gap, each of the limbs having a surface in a common plane parallel to the ais ci i tion of the permanent magnet, and ma; rotate the permanent magnet, the pole eries of the permanent magnet, the peri extension of the hollow pole arcs and the such a manner that with a rotation of the per nent magnet corresponding to about naif pole pitch the permanent magnet .in shccuited by the pole arcs of the associated ii whereas when this angle of rotation is ence the polarity is reversed.

4. A magnetic clamping appliance coi' a rotatable and substantially cylindrical p nent magnet, which is polarised transverl Yits axis of rotation, two soft iron the work-holding surface, and means the magnet with respect to the limbs i sition in which its flux in chortcire limbs, each limb having a hollow 3; arc, and the two limbs embracing tir diametrically opposite positions cylindrical air gaps co-axial t tation of the magnet.

5. A magnetic clamping apio in claim 4, in which the perm flattened on two diametrically fiat surfaces thereby formed bei parallel to the lines of force p se. body of the magnet.

6. A magnetic clamping appliance a plurality of substantially cylindrical nent magnets, each polarised axis, a plurality oi!A soft iron limbs, faces lying in a common plane to fori holding surface, and each having a. helio i drical pole arc, two limbs being asscclnt each magnet and being placed on mame@ opposite sides thereof so that the pcie cylindrical air gaps co-axial with t rotation of the magnet, and means for all the magnets together through the the pole peripheries of the permanent me the peripheral extension of the hollow pcie and the distances between the h mensioned in such a manner that with e. of the permanent magnets corres about half the pole pitch the perni@ are shortcircuited by the pole area ciated limbs, whereas when this an@ es exceeded, the polarity is reversed.

7. A magnetic clamping appliance c of a plurality of units, each compri stantially cylindrical rotatable perinan net, which is polarised transverseiy to two soft iron limbs, each of the limbs T surface lying in a common plane axis of the magnet for forming the work holding surface, and eaizh limb having a cylindrical hollow pole arc forming with the magnet a. cylinin claim 4 having a projection suitable for gripping in a vice.

9. A magnetic clamping appliance as claimed in claim 4 having a projection suitable for gripping in a vice and connected with the unit so as to be rotatable relative to it and means for xing the projection in various angular positions.

JULIUS RING. o'r'ro nLocK. 

